Conventional "Cardiac Bypass" Procedures
Various medical procedures have been developed for treating particular abnormalities of the heart and vascular system at least in part by temporarily arresting the heart from beating, isolating the heart from systemic blood circulation, supporting the systemic blood circulation via an external cardiopulmonary bypass pump, and performing surgical operations directly on the stopped heart. This general method is herein referred to interchangeably as a "cardiac bypass" or "cardiopulmonary bypass" procedure. Examples of more particular surgical treatments which use such cardiac bypass procedures include, without limitation: coronary artery bypass graft surgery ("CABG"); valve replacement surgery; cardiac transplantation sargery; and a procedure known as the "maze" procedure wherein conduction blocks are surgically formed in the wall of one or both of the atria in order to prevent atrial fibrillation.
Conventional techniques for performing such "cardiac bypass procedures" generally include cutting through the sternum in the chest cavity using well known "sternotomy" techniques, spreading open the rib cage, retracting the lungs from the region of the heart, and directly exposing the heart to the surgeon. One of various known cardioplegia agents may be used to temporarily arrest the heart from beating. Further to the bypass procedure, an external cross clamp is generally used to occlude the aorta in the region of the arch between the aortic root and the carotid arteries. With the cross-clamp in this position, both the left heart chambers and the coronary arteries into the heart are isolated from the systemic arterial circulation while the carotid arteries are fed with the blood flow from the bypass pump. In addition, flow from the superior and inferior vena cava is also temporarily diverted from the heart to the pump, usually by externally tying the vena caval walls onto venous pump cannulae. Such conventional cardiac bypass procedures as just describe which involve performing a sternotomy are hereafter referred to interchangeably as "open chest" or "open heart" procedures.
Minimally Invasive Cardiac Bypass Catheter Systems
Recent advances have been made in the field of "cardiac bypass procedures" which include the use of novel catheter assemblies which are adapted to temporarily arrest and bypass the heart without the need for direct cross-clamping or externally tying the vena cavae. Such assemblies are generally herein referred to by the terms "minimally invasive catheter bypass systems," or derivatives of these terms, and generally include an arterial catheter, which isolates the left heart chambers from systemic arterial circulation beyond the aortic root, and a venous catheter, which isolates the right heart chambers from venous circulation from the vena cavae. Further to the intended meaning, such minimally invasive catheter bypass systems may be used during open chest procedures requiring a stemotomy, as well as during other cardiac bypass procedures which otherwise alleviate the need for such sternotomies, such as for example procedures known as "port access" procedures.
One particular example of a previously known "minimally invasive cardiac bypass system" uses an arterial catheter which occludes the aorta from systemic arterial circulation with an inflatable balloon located on the outside surface of the catheter's distal end portion which is positioned within the aorta. The arterial catheter further includes a cannula with lumens and distal ports which provide for cardioplegia agent delivery and venting of the left ventricle, respectively, while the heart is isolated from systemic circulation with the inflated balloon on the outer surface of the arterial catheter. Further to this known system, a veincus catheter is further provided and uses a balloon in each of the superior and inferior vena cava. The venous catheter balloons inflate to occlude these great veins and thereby isolate the right heart chambers from systemic venous blood flow. Moreover, the venous and arterial catheters which combine to form minimally invasive cardiac bypass catheter systems engage to inlet and outlet ports, respectively of a cardiopulmonary bypass pump, which pump may be further considered a part of the overall system. One such known pump which is believed to be particularly usefull in cardiac bypass procedures, including minimally invasive bypass procedures, is known as the "BioPump", Model Number "BP80", which is available from Medtronic, Inc.
Further to the description for the minimally invasive cardiac bypass system example just provided above, the terms "proximal" and "distal" are herein used throughout this disclosure as relative terms. In the context of describing a device or catheter used in s.ch a system, the term "proximal," such as in the phrase "proximal end", is herein intended to mean toward or closer to a user such as a physician, whereas the term "distal," such as in the phrase "distal end" is herein intended to mean away from or further away from the user. However, if and where the terms "proximal" and "distal" are herein used in the context of describing anatomical structures of the cardiovascular system or physiological blood flow, the term "proximal" is herein intended to mean toward or closer to the heart, whereas the term "distal" is herein intended to mean away from or further from the heart. Furthermore, the terms "upstream" and "downstream" are also relative terms which may be herein used interchangeably with "proximal" or "distal", respectively, in the anatomical or physiological context just described.
According to the known minimally invasive cardiac bypass catheter systems and methods, the heart is usually put on "partial bypass" prior to "complete bypass". The terms "partial bypass" are herein intended to mean a condition wherein the heart is beating and pumping blood throughout the body's circulation prior to inflating the balloons on the arterial and venous catheters, and wherein some blood is also aspirated from the vena cavae through the venous catheter, sent through the cardiopulmonary bypass pump, and infused into the arterial circulation through the flow ports along the arterial catheter. The terms "complete bypass" or "full bypass" or derivatives thereof are therefore herein intended to mean a condition wherein the heart is substantially isolated from systemic venous and arterial circulation by means provided by the venous and arterial catheters, respectively, such as for example by inflating balloons on the exterior surfaces of such venous and arterial catheters to thereby totally occlude the vena cavae and aorta, also respectively, as described above.
According to these definitions for partial and full bypass just provided, a patient is therefore put on partial bypass by first positioning the venous and arterial catheters at predetermined locations along the vena cavae and aorta, respectively, such that the associated flow ports may provide for the aspiration or infusion of blood, respectively, and such that balloons on the catheter outer surfaces may be thereafter inflated to isolate the right and left heart chambers, also respectively, during full bypass. The procedure for subsequently weaning a patient from partial bypass to full bypass according to the known minimally invasive cardiac bypass system example described above generally proceeds as follows.
Cardioplegia agent is delivered during partial bypass in order to begin reducing the cardiac function ultimately toward the temporarily arrested state. The external balloons are inflated to occlude the vena cavae and isolate the right heart from systemic venous circulation prior to inflating the arterial catheter's balloon to isolate the left heart from systemic arterial circulation. During this "weaning" period, the bypass pump circulates the blood aspirated from the vena cavae while the heart continues to pump a declining volume of residual blood from the coronary sinus, right heart chambers, pulmonary circulation (including lungs), and left heart chambers. As the residual volume of blood pumping through the heart declines, and as the cardiac function continues toward temporary arrest under cardioplegia effects, the balloon on the exterior surface of the arterial catheter is then inflated to occlude the aorta and finally achieve full or complete bypass.
Upon inflating the arterial balloon and totally occluding the aorta during the "weaning" period onto full bypass as just described, additional cardioplegia agent delivery continues distally of the inflated balloon. However, it has been observed that "back pressure" on the cardioplegia delivery cannula during cardioplegia agent delivery, together with the pressure from the beating heart against the totally occluded aorta, may push the arterial balloon downstream along the aorta. As a result, a user may be required to reposition the balloon at the initially desired location along the ascending aorta between the aortic root and the carotid arteries. It is believed that the repositioning of the arterial balloon in response to this pressure response may be performed while the balloon is inflated, or during subsequent iterations of positioning and then inflating in order to adjust for the observed post-inflation movement.
Still further to the known "minimally invasive cardiac bypass systems," weaning a patient off of "complete bypass" and off of the cardiopulmonary bypass pump while reestablishing physiological cardiac output generally requires deflation of the external balloon on the external surfaces of the arterial and venous catheters. However, some patients have been observed to present complications while cardiac function is being reestablished, which complications may require returning the patient back to a full bypass condition. Therefore, patients are generally kept in surgery for a prolonged period of time subsequent to deflating the balloons on the bypass system catheters and after reestablishing the cardiac function in order to observe the heart's recovery. In cases where such patients are required to be put back onto cardiac bypass, the balloons must be repositioned at their desired location and then reinflated to isolate the heart. Particularly regarding the occlusion balloon on the external surface of the arterial catheter, this reinflation while the heart is pumping may present the same repositioning issues as previously described above.
It is further believed that the arterial balloon repositioning which may be required during use of arterial catheters according to the known minimally invasive cardiac bypass systems may present a cumbersome and potentially dangerous detriment to the efficiency and safety of the overall minimally invasive cardiac bypass procedure.
"Beating-Heart" CABG Procedures
Various methods related primarily to CABG procedures have also been disclosed which are performed without placing the heart on cardiopulmonary bypass or otherwise in a pressurized blood field.
For example, even conventional open chest CABG procedures have been disclosed for forming a proximal anastomosis between a bypass graft and an aorta without isolating the pressurized blood field in the aorta from the entire region along flow path in the aorta where the anastomosis is to be formed. In particular, one such method uses a "side-clamp" surgical tool which is adapted with two apposable, curved arms that are adapted to squeeze and clamp-off only a portion of the aortic wall. This "bite" of the aortic wall is thereby isolated from the blood field by way of the side-clamp. Thus an aperture may be formed or "punched" through the aortic wall along the isolated bite and the proximal anastomosis may be completed at that aperture without significant loss of blood from the aorta. However, it is believed that such externally clamping of the aorta may present some degree of undesirable mechanical trauma to the aortic wall tissue as the aorta is in part crushed and deformed by such clamps, and furthermore that such external clamping may give rise to various procedural complications during some CABG procedures.
Recent advances have also been made also principally in minimally invasive CABG procedures which also allow a bypass graft to be anastomosed proximally to an aorta and distally to a coronary artery without the need to place the patient on cardiopulmonary bypass. One such disclosed procedure requires particular minimally invasive device assemblies and methods that are adapted to form the anastomoses while the heart is beating. One detailed device which has been disclosed for use in such procedures includes a "perfusion bridge" for use in perfusing a region of a coronary artery while substantially isolating a distal anastomosis site along that region from the perfused arterial blood. Another detailed device for use in such procedures provides a structure or "foot" for engaging and substantially securing the motion of the beating heart while a distal anastomosis is formed, such according to at least one disclosed mode by use of suction.
At least one other known procedure involves particular devices and methods which are adapted to temporarily arrest or otherwise reduce a heart beat for relatively short periods of time, without cardiopulmonary bypass support, and only while various steps for forming a distal graft anastomosis are performed in a CABG procedure. According to this method, the heart is temporarily "stunned" from beating, such as by stimulating the vagal nerve, while forming an anastomoses and rapidly recovers to resume beating quickly after the anastomosis is completed. According to this prior disclosure, it is believed that the patient tolerates such short interruptions or reductions in the heart beat sufficiently to not require cardiopulmonary bypass support.
Such novel procedures as just described which either temporarily reduce or arrest the heart without cardiopulmonary bypass support are herein generally referred to as "semi-beating heart" procedures. Moreover, the terms "beating heart" in relation to the various assemblies and methods described are herein intended to generically mean any procedure operating in a pressurized aortic blood field without the heart on cardiopulmonary bypass. Therefore, such "beating heart" assemblies and methods are intended to encompass both the "semi-beating heart" assemblies and methods just specifically described, in addition to the more specific applications of devices and methods wherein a heart is substantially beating in the normal physiologic rhythm for a given patient. Moreover, such "beating heart" procedures as just described, it is appreciated that related minimally invasive catheter bypass systems and methods may be used to perform such procedures either in an "open chest" mode incorporating a sternotomy to directly expose the heart, as well in "port access" mode that otherwise alleviates the need for such sternotomies.
Further more detailed device assemblies and methods for performing at least in part beating heart or semi-beating heart CABG procedures, such as of the types just described, are variously disclosed in the following U.S. Patent References: U.S. Pat. No. 5,776,154 to Taylor et al.; U.S. Pat. No. 5,769,870 to Salahieh et al.; U.S. Pat. No. 5,727,569 to Benetti et al.; U.S. Pat. No. 5,651,378 to Matheny et al.; U.S. Pat. No. 5,730,757 to Benetti et al.
There is still a need for an endolumenal medical device system and method for isolating a proximal anastomosis site from a pressurized aortic blood field so that a proximal anastomosis may be formed between an arterial bypass graft and the aorta without externally clamping the aorta and without substantial loss of the pressurized aortic blood during a "beating heart" or "semi-beating heart" arterial bypass graft procedure.
There is also a need for an endolumenal medical device system and method which allows a proximal anastomosis site to be isolated from a pressurized aortic blood field during a "beating-heart" or "semi-beating heart" arterial bypass graft procedure and which is also adapted to isolate the proximal anastomosis site and heart from systemic blood flow during a "stopped-heart" cardiac bypass procedure.